The present invention relates to a polyamide-based sausage casing. It is contemplated, in particular, for sausage production on a relatively small scale in which stuffing is performed not automatically, but manually. The casing is especially suitable for cooked-meat sausages and scalded-emulsion sausages.
Fiber-reinforced cellulose casings which are produced by the viscose process and are provided with a water-impermeable inner coating have the largest share in the production of cooked-meat sausages and scalded-emulsion sausages. They are followed in second place by the casings made of thermoplastics, in particular of polyamide or vinylidene chloride copolymers. For sausage production on an artisanal scale, the internally-coated fiber-reinforced cellulose casings are considerably better suited than the thermoplastic casings.
Cooked-meat sausages and scalded-emulsion sausages are, after stuffing, scalded in water or steam at about 80° C., occasionally also at from 110 to 130° C. In the course of this the volume of the sausage-meat emulsion increases. On cooling it then markedly decreases again. The sausage casing must adapt itself to the changing volume of the sausage-meat emulsion. In particular, the sausage casing is to contract on cooling to the extent that no wrinkles are formed. This is because sausage having a wrinkled casing is generally regarded as “no longer fresh”. Furthermore, the casing should have sufficient tension that no liquid collects under it after the scalding. A “gel deposit” of this type between casing and emulsion is likewise considered a quality defect.
Said internally-coated cellulose casings are usually softened prior to stuffing. In this process, the highly hygroscopic cellulose is saturated with water. The water absorption is generally from 110 to 140% by weight. At the same time the casing swells and becomes highly supple. In this state, it is stuffed with the emulsion. After the scalding and cooling, the sausage is dried. In the course of this, the casing releases again the majority of the absorbed water. However, because of the impermeable inner coating, virtually no moisture can escape from the sausage-meat emulsion. During the drying, the cellulose layer contracts greatly, so that the casing tightly encloses the cooled sausage-meat emulsion. Wrinkles and gel deposit are thus prevented, even if the emulsion—as is usual with manual stuffing—was stuffed under no external pressure or at only a low pressure.
As regards their service properties, the internally coated cellulose casings are ideal for manual stuffing. However, a disadvantage with these casings is the complex and expensive production by the viscose process. In this process, a cellulose xanthogenate solution is firstly applied to the fiber reinforcement which has been preshaped to form a tube. The cellulose xanthogenate is then precipitated in dilute sulfuric acid and regenerated to form cellulose hydrate. After washing and drying the casing, a polymer dispersion is applied to its inside, which polymer dispersion then gives the water-impermeable coating.
In contrast, cooked-meat sausage casings and scalded-emulsion sausage casings may be produced much more simply and inexpensively by extrusion blow-moulding of thermoplastics. Casings of biaxially stretched polyamide have achieved some importance here. Thus, DE-A 28 50 182 (=GB-A 2 035 198) describes a single-layer biaxially stretched casing of an aliphatic polyamide whose glass transition point in the dry state is at least 48° C. and which may be decreased after water absorption to at least 3° C., preferably to −5° C. Polyamides which are specifically disclosed are nylon 6 (=polycaprolactam), nylon 7, nylon 6,6 (=polyamide of hexamethylenediamine and adipic acid), nylon 6,10 (=polyamide of hexamethylenediamine and sebacic acid). According to DE-A 28 50 181, the casing additionally comprises an ionomer resin, a modified ethylene-vinyl acetate copolymer and/or a quaternary copolymer containing units of ethylene, butylene, an aliphatic ethylenically unsaturated (C3-C5)carboxylic acid and an ester of this carboxylic acid with a (C1-C8)alkanol. This casing, after the initial cutting of the sausage, shows a reduced tendency to tear propagation. The polyamide casing according to DE-A 32 27 945 (=U.S. Pat. Nos. 4,560,520 and 4,601,929) is said to have the same advantage.
EP-A 0 065 278 discloses a single- or multilayer, shrinkable flat film in which the layer or at least one layer consists of polyamide. The polyamide layer comprises a linear aliphatic (co-)polyamide and a partially aromatic (co-)polyamide. The linear aliphatic (co-)polyamide can be partially or completely replaced by an elastomeric component, such as polybutadiene, polyurethane rubber or nitrile rubber. The film is additionally stretched, but not thermoset, since it is to have a high shrinkability and high shrinkage force. These properties are caused by the special polymer combination in the polyamide layer.
In order that the finished cooked-meat sausages and scalded-emulsion sausages lose as little weight as possible during storage, a permeability to water or water vapor as low as possible is also wanted for the casings made of thermoplastics. However, many polyamides can absorb up to 10% by weight of water. Pure polyamide casings are therefore less suitable. In order to make up for this disadvantage, multilayer casings have been developed which additionally comprise (at least) one layer of a water-vapor-impermeable polymer. Thus, the biaxially stretched casing according to EP-A 573 306 consists of a middle polyamide layer and an inner layer and an outer layer of a water-vapor-barrier polymer, eg. a polyolefin. DE-A 40 17 046 likewise discloses a three-layer biaxially stretched and thermoset casing. Here, the outer layer consists of aliphatic polyamide and/or copolyamide, the middle layer consists of polyolefin and an adhesion-promoting component and the inner layer consists of aliphatic and/or partially aromatic (co-)polyamide.
After heating to temperatures of about 80° C. or above, as are attained on scalding the sausage, the casings begin to shrink. Owing to this thermal shrink, the circumference of the casing generally decreases by from 5 to 20%. The extent of the contraction also depends here on the conditions in the preceding thermosetting. Usually, during the thermosetting a transverse shrinkage of the tube of up to 40% has already taken place. Simultaneously, the diameter of the tube becomes more uniform. On scalding the sausage, the thermal shrinkage begins virtually immediately. This leads to the tension of the casing being greatest at the beginning of the only a relatively low residual elasticity.
In sausage production on an industrial scale, this problem is solved by stuffing the emulsion under high pressure. A stuffing pressure of from 20 to 40 kPa is usual, depending on the caliber of the sausage casing. However, specially constructed stuffing machines are necessary for this. In this manner, a first (partially) elastic extension of the casing is achieved. The elastic force resulting in the course of this is, as is also the thermal shrinkage force, partially diminished during the scalding. The remaining force is then generally just sufficient to ensure tight and wrinkle-free fitting of the casing.
However, without special stuffing machines, a high stuffing pressure cannot be achieved. Manually stuffed polyamide casings are therefore, after the scalding and cooling, generally wrinkled and less attractive. Therefore, in the artisanal sector, the internally-coated cellulose casings described at the outset continue to be used.